1. Technical Field
This application relates to the field of adjusting mechanical systems, and more particularly to the field of measuring vibration and using the measurement to provide suggested adjustments to reduce the vibration.
2. Description of Related Art
Mechanical system often contain a plurality of shafts that rotate at relatively high speeds. In some cases, imbalance of the shaft may cause unacceptable vibrations. For example, in a helicopter system with many high speed shafts, a vibration of two ips (inches per second) renders the helicopter unflyable. Even shaft vibration as slow as ½ ips may make flying in a helicopter uncomfortable. Thus, it is desirable to be able to eliminate or at least reduce vibrations caused by shaft imbalance.
In some cases, shafts are provided with a provision for inserting weights at the end thereof in the form of bolts and/or washers. There may be a number of possible bolts of different fixed weights such as one grams, two grams etc. and, similarly, there may be a number of possible washers of different fixed weights such as ¼ gram, ½ gram, etc. Adjustments may be made by placing some combination of bolts and/or washers into the adjusting positions at the end of the shaft. However, it is usually difficult to determine manually how much needs to be added to each location. Using trial and error is impractical because, in the first place, determining an effective adjustment using trial and error requires restarting the machine and remeasuring the vibrations each time an adjustment is made and, in the second place, the number the combinations may make trial error prohibitive. For example, if there is six possible bolt hole locations and five possible weights (three bolts and/or two washers) that could go in each location, then the number of combinations we are balancing is approximately 47045881. The problem expands worse than exponential. For 12 possible bolt hole locations and similar adjustments, the total number of combination is now 2.2133×1015.
In some instances, it may be possible to use a computer to determine the appropriate adjustment for balancing the shaft. However, even if the vibrations are measured by the computer, it may not be possible to provide an exact counteracting weight since the adjusting weights are discrete amounts provided at discrete locations whereas the vibration could be any amount at any location on the shaft. In addition, a computational trial and error method may be prohibitive with a computer because, just as with the manual trial error method, the number of combinations may so large that it would be prohibitive to have a computer do calculations for all the possible combinations.
Accordingly, it is be desirable to provide a technique for determining an adjustment to balance a rotating shaft.